The present invention relates to the field of power generation. It relates in particular to a power generating device which can be connected in particular to a public AC voltage supply network and/or to an island network, as claimed in the pre-characterizing clause of the independent claim.
Nowadays, power generating devices are used mainly to generate additional electrical power for conventional electrical AC voltage supply networks and/or for supplying island networks in remote areas. One such power generating device is disclosed, by way of example, in U.S. Pat. No. 5,903,116. In this document, the power generating device has a drive unit, which is in the form of a turbine. The drive unit is coupled to a generator, which is connected to a DC voltage intermediate circuit via a passive rectifier. The DC voltage intermediate circuit is formed from two capacitors, which are used as an electrical energy store. Furthermore, the DC voltage intermediate circuit is connected to an inverter which, on the AC voltage output side, has n phases with n AC voltage connections, where, in particular, n is equal to 3. Furthermore, the DC voltage intermediate circuit is connected to a balancing apparatus, which is formed from two series-connected power semiconductor switches, with a diode being connected back-to-back in parallel with each power semiconductor switch. The junction point of the power semiconductor switches is connected via an inductance to the junction point of the two capacitors in the DC voltage intermediate circuit. Furthermore, the junction point of the power semiconductor switches is in the form of a neutral point connection, with the neutral point connection being used as a connection for a neutral point of an island network. The voltage on the two capacitors in the DC voltage intermediate circuit can be balanced by appropriate actuation of the power semiconductor switches. Furthermore, the AC voltage connections of the inverter in the power generating device are connected to a conventional filter arrangement, with the filter arrangement being connected to the electrical AC voltage supply network. A conventional filter arrangement such as this is specified, by way of example, in EP 0 682 401 A1. In this document, each AC voltage connection of a three-phase inverter is connected to a filter inductance, and each filter inductance is connected to a filter capacitor, with the junction point of the filter inductance and the filter capacitor forming a network connection.
The balancing apparatus which has been mentioned above is subject to the problem that undesirable fluctuations can occur in the DC voltage of the DC voltage intermediate circuit in the case of an alternating component, particularly if any current via the neutral point connection has a relatively high-frequency alternating component. Furthermore, any DC component in the current via the neutral point connection leads to the DC voltage intermediate circuit being charged or discharged, depending on the mathematical sign of the current. However, charging of the DC voltage intermediate circuit can lead to an unacceptably high DC voltage in the DC voltage intermediate circuit, which can lead to a flashover as a result of which the DC voltage intermediate circuit, in particular the capacitors as well as the components of the rectifier and of the inverter, may be damaged or destroyed. Furthermore, a DC component such as this as well as any alternating component that the current via the neutral point connection may have leads to a shift in the voltage relationships on the two capacitors in the DC voltage intermediate circuit. This can lead to an unacceptably high voltage on one of the capacitors, which can damage or destroy that capacitor. Any unbalance such as this can be coped with or overcome only by monitoring the voltage on each capacitor in the DC voltage intermediate circuit and by complex actuation of the power semiconductor switches, coupled to the monitoring process.
In the event of any disturbances in the electrical AC voltage supply network, a filter arrangement as mentioned above cannot keep such disturbances away from the inverter in the power generating device, by virtue of its design with a filter capacitor and a filter inductance. Furthermore, medium-frequency and high-frequency ripple control signals which are modulated onto the network voltage are substantially filtered out by a filter arrangement such as this, although ripple control signals such as these are required for information and/or control purposes, depending on the configuration of the power generating device.
The object of the invention is therefore to specify a power generating device, which is robust to disturbances in an electrical AC voltage supply network which may be connected to the power generating device. This object is achieved by the features of claim 1. Advantageous developments of the invention are specified in the dependent claims.
The power generating device according to the invention comprises a generator which is coupled to a drive unit, in particular to a turbine, and is connected via a rectifier to a DC voltage intermediate circuit, with an inverter being provided, which is connected to the DC voltage intermediate circuit and, on the AC voltage output side, has n phases with n AC voltage connections. A filter arrangement is also connected to the AC voltage connections of the inverter. According to the invention, the filter arrangement has a first filter inductance and a second filter inductance, which is connected in series with the first, for each AC voltage connection, with a filter capacitor being connected to the junction point of the first filter inductance and the second filter inductance. Furthermore, the filter capacitors are connected in a star circuit. This filter arrangement advantageously allows disturbances in an electrical AC voltage supply network which can be connected to the filter arrangement to be very largely kept away from the inverter, since the filter arrangement represents a high input impedance, seen from the electrical AC voltage supply network. Furthermore, signals which are modulated onto the network voltage of the electrical AC voltage supply network, such as ripple control signals, can pass through the filter arrangement without being significantly filtered out.
In one preferred embodiment of the power generating device according to the invention, a balancing apparatus is provided, which is connected to the DC voltage intermediate circuit and is formed from two series-connected controllable power semiconductor switches, each having a back-to-back parallel-connected diode. According to the invention, the junction point of the power semiconductor switches is connected to the star point of the filter capacitors. The star point thus advantageously forms a neutral point connection, for example for a neutral point of an island network which is to be fed in addition to the electrical AC voltage supply network. A further advantage is that any current flowing via this neutral point connection, in particular with a DC component and/or an alternating component, and in particular an alternating component of relatively high frequency, will have no significant influence on the way in which the voltage is split in the DC voltage intermediate circuit of the power generating device, so that the DC voltage which is present in the DC voltage intermediate circuit is not significantly influenced by such disturbances. Furthermore, the balancing apparatus advantageously makes it possible to set the neutral point to a potential which can be predetermined.
This and further objects, advantages and features of the present invention will become evident from the following detailed description of a preferred exemplary embodiment of the invention, and in conjunction with the drawing.